An Internet Protocol network (IP network) such as the Internet or a Wide Area Network (WAN: wide area communication network) is called, for example, substrate network, and includes various kinds of packet relay devices such as a IP router for relaying packets and an Layer 3 (L3) switch.
A related technique is disclosed in Japanese Laid-open Patent Publication No. 7-162422 or Japanese Laid-open Patent Publication No. 2008-182423.